In town, keep out of the centre of crime or sin (4)

'sin' is the definition.
Both the answer and definition are singular nouns.
Perhaps they are linked in a way I don't understand?

'in town keep out of the centre of crime' is the wordplay.
'in town keep' becomes 'bai' (I can't explain this - if you can you should give a lot more credence to this answer).
'out of' means one lot of letters goes inside another (some letters on the outside of others).
'the centre of' means to look at the middle letters.
'crime' becomes 'porno' (porno is a kind of crime).
The middle of 'porno' is 'r'.
'bai' placed around 'r' is 'BARI'.

'or' acts as a link.

Can you help me to learn more?